Microwave activated two-photon transition for remote entanglement of superconducting circuits*

Building a large scale quantum computing platform or network will most probably require to entangle distant systems that do not interact directly. This can be done by performing entangling gates between standing information carriers, used as memories or local computationnal resources, and flying ones, acting as quantum buses. In this talk, we report the realization of such gates between superconducting circuits and traveling microwave photons based on microwave activated two-photon transitions. We have implemented this protocol in a superconducting circuit architecture. Temporal and, to some extent, frequential shaping of the traveling wavepacket have been applied. We demonstrate both an entangling gate corresponding to the emission of a shaped photon conditionned on the excitation of a circuit and a swap gate corresponding to the absorption of this photon by a distant circuit. Combining both, we remotely entangle two transmon qubits with a Bell state fidelity of 73 %, limited by losses in the transmission line and decoherence of each qubit.